This Core will perform five functions in a high-quality, reliable, and cost- effective manner: 1. murine bone mineral density done serially in longitudinal experiments in live mice by dual energy x-ray absorptiometry (DXA or DEXA); 2. routine plastic embedding, sectioning and staining of undecalcified, tetracycline labeled bone for quantitative histological analysis; 3. special histological staining procedures, such as cytostaining of bone tissue for luciferase or beta- galactosidase (LacZ) activity, prevalence of bone cell apoptosis, quantification of cancellous fat cell area and diameter, and detection of double tetracycline labels in transgenic mice with a tetracycline controllable conditional promoter; 4. direction measurements of vertebral compression strength; and 5. training of key personnel from the Program Projects to read the quantitative features of tetracycline labeled bone sections. This core will teach individual personnel of the project groups how to acquire the femora and lumbar vertebrae at necropsy, measure bone histomorphometric features of tetracycline labeled bone sections. This core will teach individual personnel of the project groups how to acquire the femora and lumbar vertebrae at necropsy, measure bone histomorphometric features, and understand the histomorphometric analysis necessary to meet the goal of the projects. More than 400 murine vertebral compression studies have been performed during the past 18 months. In preliminary experiments, the correlation of spinal BMD (DEXA) with vertebral compression strength of L5 was strong (r=0.778, P <0.0001, n=67). Sixty percent of the compression strength was accounted for by changes in the BMD. We will now explore the microstructural, material, and cellular mechanisms that make up that remaining 40%. The core has also done more than 2800 murine DEXA measurements in vivo and has archived, processed of measured more than 1752 murine bone specimens during the past four years. The bone laboratory is a CAP accredited facilitated with the ability to safely archive and store tissue and data. Bone densitometry histomorphometry and compression strength results will be appended to a relational database for efficient utilization by the principal investigators of each project.